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TUESDAY, September 25, 2012 (HealthDay News) — The link between chronic stress and weight gain is much stronger in black girls than white girls, and may help explain why black girls are more likely to be overweight than white girls, according to a new study.

In the United States, the obesity rate in blacks is 50 percent higher than in whites, the researchers noted. This difference is apparent even in childhood, particularly among female teens.

Researchers looked at obesity rates among nearly 2,400 black and white girls, who were followed for up to 10 years beginning at age 10 as part of the National Heart, Lung, and Blood Institute's Growth and Health Study. The researchers also looked at the girls' stress levels over that time.

The study was published online in the journal Annals of Behavioral Medicine.

Over the study period, more black girls were overweight or obese than white girls. Even though black girls reported less stress than white girls, the effect of chronic stress on body-mass index was stronger among black girls, said A. Janet Tomiyama, of the University of California, Los Angeles, and colleagues. Body-mass index, or BMI, is a measurement of body fat based on height and weight.

A one-unit increase in chronic stress resulted in a 0.8-unit BMI increase every two years among black girls, compared with a 0.55-unit BMI increase among white girls.

"Psychological stress may lead to weight gain through behavioral pathways, such as increased food consumption and sedentary lifestyles, but also directly through prolonged exposure to biological stress mediators such as cortisol," the researchers wrote in a journal news release.

Blacks tend to experience greater psychological stress than whites partly because of perceived racial discrimination, the researchers said. The findings suggest that stress may play a major role in the obesity epidemic as well as racial disparities in obesity rates, they added.

Although the study found a link between chronic stress and obesity, it did not prove cause-and-effect.